In situ precipitation of gold nanoparticles onto glass for potential architectural applications

The optical properties of in situ deposited gold nanoparticle coatings are investigated for potential application in architectural glass. It is found that the optical properties of the coating can be controlled by the pH of the deposition solution. At a pH of 5.1, the color of the coatings develops from pink, through violet, to blue in transmission. This is due to a plasmon resonance peak at 520 nm from isolated particles, and one at about 700 nm due to near-field dipole interactions, with an intermediate zone of the coexistence of the two, which produces the violet color. However, the two peaks do not coexist in the spectra of coatings produced at pH 8.0 or 10.0, with the peak due to the 520 nm resonance being swamped by the development of the resonance due to particle-particle interactions. In all cases the 700 nm peak could be broadened and red-shifted by increasing the deposition time. The reasons for these differences are explored and are shown to be attributable to the smaller, more aggregated morphology of nanoparticles precipitated at the higher pHs. The wavelength of maximum plasmon resonance is examined as a function of the volume fraction of nanoparticles. Significant deviations from the well-known Genzel-Martin analytical model are observed. The reasons for deviation of the model are discussed. Finally, it is shown how coatings that are blue or blue-gray in transmission can be obtained by exploiting this deviation. Such coatings may be more suitable for architectural application than the conventional pink-hued coatings obtained with colloidal gold nanoparticles.